The present invention relates to a drive assembly with an electric motor, and more particularly to an electric motor that can be stopped immediately at any time in the event of a malfunction of the drive circuitry.
An electric motor should be stopped immediately when a controlled operation of the electric motor is no longer possible. A drive may malfunction for failure to receive drive pulses. The drive then lacks a torque and can therefore no longer be controlled to operate as a generator brake. In such situations, the kinetic energy stored in the drive and the coupled mechanism can put people at risk or damage machine parts. However, drive systems of the afore-described type are typically provided with additional features designed to stop the electric motor and the connected mechanical components. On one hand, the motor can be braked mechanically by applying a mechanical brake. Such brakes normally operate on vertical axles of machines and oftentimes also on horizontal axles. Service brakes and/or holding brakes can be provided depending on the application. Service brakes have a significantly greater braking torque than holding brakes. With linear axles, service brakes are predominantly attached directly to the load, whereas holding brakes typically form an integral component of the motor.
The effective braking torque of mechanical brakes typically increases with decreasing motor speed. Mechanical brakes are also known to have a relatively long delay time, i.e., a time in the order of 40 milliseconds can pass from the command to apply the brake until the brake actually engages.
Drive systems of the afore-described type can also include an armature short-circuit brake. An armature short-circuit brake can be implemented by using external components, for example components controlled by a relay. The armature short-circuit brake can also be an integral component of a motor controller, as disclosed for example in European patent publication EP 0 742 637.
An armature short-circuit brake typically has a high braking torque at a high motor speed, while providing only a limited braking action at a low motor speed. The effective braking torque therefore decreases with decreasing motor speed. However, an armature short-circuit brake typically has a fast reaction time, so that an integrated electronic armature short-circuit can achieve a reaction time of only 5 milliseconds.
It would therefore be desirable and advantageous to provide an improved drive system with an electric motor, which obviates prior art shortcomings and is able to quickly brake the motor and/or drive system without placing a burden on the motor components and the control electronics.